Injecting machines are mainly used with shaping molds for forming products. Materials are heated, extruded and then fed into a mold. Conventionally plastic material is used due to a low melting point, small grain sizes and preferred uniformity. Moreover, in the process of storage and injection, the material has no bubble therein.
Currently, many products, for example, computer casings, use metals as material (for example, aluminum) for replacing plastic material. However, metals are heavy and dense than plastics. Moreover, the grains of the metal after melting are not so uniform as plastic grains. Thereby, conventionally, a feeding screw rod with screw threads at the middle section is used to feed material, but this will induce bubbles to be accumulated in the metal material. As a result, the surface of the product is not uniform or gaps are formed in the wall of the product.
Referring to FIG. 1, a prior art thixomolding method disclosed in U.S. Pat. No. 5,040,589 is illustrated. In this conventional way, metal grains are machined into a great deal of chips. Thereby, in transferring by the feeding screw rod, it is heated as a mixing structure containing solid grains and liquids, and for a long period, the material becomes a viscous material. The defect of this prior art is that the chip must be retained in a viscous condition, neither liquid nor solid can exist therein. This is very difficult, especially to control the temperature in operation.
Referring to FIG. 2, a first class rheomolding method disclosed in U.S. Pat. No. 6,405,784 is shown. In this prior art way, the device used is improved from the conventional used one. Grain-like material is melt as liquid in a transversal material feeding cylinder. Then the material is fed to a following inclined cylinder by using a piston. Then the melt material is pushed into a mold by the piston.
Referring to FIG. 3, a first class rheomolding method disclosed in U.S. Pat. No. 5,501,266 is shown. In this prior art way, the device used is improved from the conventional used one. The block-like metal is melt and thus is supplied to a screw rod so that melt material can be injected into a mold.
In above two Rheomolding methods, the melting metal must be retained in a viscous state from a liquid state for being placed in the mold to form a desired shape. Thereby, the temperature must be reduced from a high temperature. However, this is difficult in a long and continuous operation. To control the metal in a steady state is very difficult. Moreover, these two methods generate more bubbles than the prior art method so that the smoothness of the product is not preferred.